Method and apparatus for signaling aperiodic channel state indication reference signals for lte operation

ABSTRACT

A UE can receive Zero Power Channel State Information Reference Signal (ZP-CSI-RS) configuration information for an aperiodic ZP-CSI-RS of a serving cell. The UE can receive Downlink Control Information (DCI) on a physical control channel in a subframe of the serving cell. The DCI can indicate whether a Physical Downlink Shared Channel (PDSCH) of the UE in the subframe of the serving cell is rate-matched around resource elements indicated by the ZP-CSI-RS configuration information. The UE can decode the PDSCH in the subframe of the serving cell based on rate-matching around the resource elements indicated by the ZP-CSI-RS configuration when the DCI indicates the PDSCH of the UE is rate-matched around the resource elements indicated by the ZP-CSI-RS configuration.

BACKGROUND

1. Field

The present disclosure is directed to a method and apparatus forsignaling aperiodic channel state indication reference signals. Moreparticularly, the present disclosure is directed to a method andapparatus for signaling aperiodic channel state indication referencesignals for Long Term Evolution (LTE) operation in unlicensed spectrum.

2. Introduction

Presently, users use portable devices, otherwise known as User Equipment(UE), such as smartphones, cell phones, tablet computers, selective callreceivers, and other wireless communication devices, on LTE networks.Users use the UEs to download files, music, e-mail messages, and otherdata, as well as to watch streaming video, play streaming music, playgames, surf the web, and engage in other data intensive activities.Because of large amounts of downloaded data as well as large amounts ofusers, LTE carriers can now use unlicensed spectrum to complement thebandwidth of their LTE networks to provide faster data to users. Thisallows the users to download data faster on their portable devices. Forexample, unlicensed spectrum can include spectrum at 5 GHz (e.g. used byWiFi) and other unlicensed spectrum. LTE technology can be deployed inunlicensed spectrum using the carrier aggregation framework wherein theprimary cell uses licensed spectrum, and a secondary cell is deployed inthe unlicensed spectrum. Transmissions on the unlicensed carriertypically have to follow Discontinuous Transmission requirements (DCTrequirements) due to regulatory requirements and due the need toco-exist with other wireless systems operating in the same spectrum,such as Wi-Fi systems, LTE devices, such as User Equipment (UE), andbase stations, such as Enhanced Node-B's (eNBs). In some regulations, aLTE device may be required to perform listen-before-talk (LBT) prior totransmitting on a carrier. If the device finds that the channel is busy,then it should defer its transmission until the carrier become clear.For DCT, after acquiring the channel, a LTE device can continuouslytransmit for X ms, where X=4 ms for some regulations and X=up to 13 msfor other regulations. After X ms the device has to cease transmissionfor some duration, sometimes referred as an idle period, perform LBTchannel assessment, and reinitiate transmission only if LBT issuccessful. As a result of the discontinuous transmission, transmissionof frames and reference signals in unlicensed spectrum can be aperiodic.

Unfortunately, because the transmission of frames and reference signalsare aperiodic, a UE has problems determining how to measure a referencesignal to ascertain channel state information to report it to a basestation.

Thus, there is a need for a method and apparatus for signaling channelstate information reference signals for LTE operation.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of thedisclosure can be obtained, a description of the disclosure is renderedby reference to specific embodiments thereof which are illustrated inthe appended drawings. These drawings depict only example embodiments ofthe disclosure and are not therefore to be considered to be limiting ofits scope.

FIG. 1 is an example block diagram of a system according to a possibleembodiment;

FIG. 2 is an example signal flow diagram according to a possibleembodiment;

FIG. 3 is an example signal flow diagram according to a possibleembodiment;

FIG. 4 is an example illustration of subframes of a way a user equipmentcan report channel state information according to a possible embodiment;

FIG. 5 is an example illustration of subframes of another way a userequipment can report channel state information according to a possibleembodiment;

FIG. 6 is an example illustration of subframes of another way a userequipment can report channel state information according to a possibleembodiment;

FIG. 7 is an example block diagram of an apparatus according to apossible embodiment;

FIG. 8 is an example block diagram of a base station according to apossible embodiment; and

FIG. 9 is an example illustration of a subframe according to a possibleembodiment.

DETAILED DESCRIPTION

Embodiments can provide for a User Equipment (UE) that can receiveDownlink Control Information (DCI) from a base station. The DCI cancontain a Channel State Information (CSI) request on a physical controlchannel in a subframe of a first serving cell. The CSI request candirect the UE to perform CSI measurements for at least one aperiodicChannel State Information Reference Signal (CSI-RS) of a second servingcell. The UE can ascertain CSI-RS resources in a subframe of the secondserving cell based on at least the DCI contents. The UE can determineCSI based on the ascertained CSI-RS resources. The UE can then send thedetermined CSI to the base station.

Embodiments can further provide for a UE that can receive Zero PowerChannel State Information Reference Signal (ZP-CSI-RS) configurationinformation for an aperiodic ZP-CSI-RS of a serving cell. The UE canreceive DCI on a physical control channel in a subframe of the servingcell. The DCI can indicate whether a Physical Downlink Shared Channel(PDSCH) of the UE in the subframe of the serving cell is rate-matchedaround resource elements indicated by the ZP-CSI-RS configurationinformation. The UE can decode the PDSCH in the subframe of the servingcell based on rate-matching around the resource elements indicated bythe ZP-CSI-RS configuration when the DCI indicates the PDSCH of the UEis rate-matched around the resource elements indicated by the ZP-CSI-RSconfiguration.

Embodiments can further provide for signaling channel state informationreference signals for Long Term Evolution (LTE) operation in unlicensedspectrum. For example, embodiments can provide mechanisms in Release 13LTE to deliver downlink CSI-RS and associated control information from amulti-antenna base station (eNB) to a User Equipment (UE) to assist theeNB in its multi-antenna precoding operations, as applied to LTELicense-Assisted Access (LTE-LAA) deployment scenarios in which theCSI-RS's are transmitted to the UE on a secondary carrier operating inunlicensed spectrum. Access to the unlicensed spectrum at any given timeand location can depend on whether the unlicensed spectrum is not beingused by others, so the eNB may not rely on transmitting the CSI-RS on aduty cycle as is done in previous LTE releases.

The UE-specific configuration of the CSI-RS resources can be done onhigher layers, and one problem solved can be how to notify the UE ofwhich received subframe contains the CSI-RS transmissions. According toa possible embodiment, when the UE receives a DL grant on the unlicensedcarrier in a subframe, the grant contains a CSI-RS request, so the UEknows that an aperiodic CSI-RS transmission is in the subframe. The UEmeasures the CSI-RS and reports the CSI to the eNB. The CSI report caninclude one or more of CQI (Channel Quality Information), RI (RankInformation), PMI (Precoding Matrix Indication), PTI (Precoder TypeIndication) and/or other information.

FIG. 1 is an example block diagram of a system 100 according to apossible embodiment. The system 100 can include a first UE 110 and abase station 120, such as an Enhanced Node-B (eNB). The first UE 110 andthe base station 120 can communicate on different cells 130 and 140. Thecell 130 can be a first cell, such as a primary cell and the UE 110 canbe connected to the primary cell. The cell 140 can be a second cell,such as a secondary cell. Furthermore, the second cell 140 can be a cellthat operates on unlicensed spectrum. The cells 130 and 140 can also becells associated with other base stations, can be a macro cells, can bemicro cells, can be femto cells, and/or can be any other cells usefulfor operation with a LTE network. The system 100 can also include asecond UE 112 that can communicate with the base station 120 on cells132 and 142 in a similar manner to the first UE 110. The UE's 110 and112 can be any devices that can access a wireless wide area network. Forexample, the user devices 110 and 112 can be wireless terminals,portable wireless communication devices, smartphones, cellulartelephones, flip phones, personal digital assistants, personal computershaving cellular network access cards, selective call receivers, tabletcomputers, or any other device that is capable of operating on awireless wide area network.

FIG. 2 is an example signal flow diagram 200 according to a possibleembodiment. The signal flow diagram 200 shows signals and operations ofthe UE 110 and the base station 120. From the base station perspective,at 210, the base station 110 may or may not perform a Listen-Before-Talk(LBT) procedure to determine if a carrier is clear for a carrierfrequency corresponding to a second serving cell, such as second cell140, prior to sending the aperiodic CSI-RS on the second serving cell.The LBT procedure can be performed to determine if the carrier is clearfor transmissions.

At 220, the base station 120 can transmit DCI in a subframe to the UE110. The DCI can contain a CSI request on a physical control channel ina subframe of a first serving cell, such as the first cell 130. The CSIrequest can direct the UE 110 to perform CSI measurements for at leastone aperiodic CSI-RS of the second serving cell. The DCI can include anindication of resources for the aperiodic CSI-RS in a subframe of thesecond serving cell. The second serving cell may or may not operate inan unlicensed spectrum.

Contents of the DCI for determining the CSI-RS resources can be in a CSIrequest field and/or another field of a control channel. The DCI canalso indicate granted resources on which the CSI is sent by the UE 110to the base station 120. For example, the base station 120 can indicateto the UE 110 which resources it is granted for sending the CSI to thebase station 120. The CSI-RS resources in the subframe can be based on ahigher layer signaled CSI-RS configuration for aperiodic CSI-RStransmission, where the higher layer can be a layer higher than aphysical layer.

At 240, the base station 120 can send the CSI-RS based on the indicatedresources for the aperiodic CSI-RS in the subframe of the second servingcell. At 260, the base station 120 can receive, in another subframe, amessage containing the requested CSI from the UE 110.

From the UE perspective, at 220, the UE 110 can receive DCI from thebase station 120. The DCI can contain a CSI request on a physicalcontrol channel in a subframe of a first serving cell. The CSI requestcan direct the UE to perform CSI measurements for at least one aperiodicCSI-RS of a second serving cell. Receiving DCI can include receivingCSI-RS configuration information for the at least one aperiodic CSI-RS.DCI contents for determining the CSI-RS resources can be in at least oneof a CSI request field and another field of a control channel. The DCIcan also indicate granted resources on which the CSI is sent by the UE110 to the base station 120. The DCI, such as DCI format 0 or other DCIformat (e.g. DCI format 1A), may contain fields such as “aperiodic CSIrequest,” “resources for transmissions,” “modulation and coding scheme,”and other fields. The DCI can be transmitted by the base station 120 andreceived by the UE 110 on control channels, such as a Physical DownlinkControl Channel (PDCCH), an Enhanced PDCCH (EPDCCH), and/or other typesof control channels, where the DCI can be content of the controlchannel. The DCI can also contain Channel State Information InterferenceMeasurement (CSI-IM) configuration information for a CSI-IM of theserving cell and a set of resource elements used for determining CSI canbe indicated by the CSI-IM configuration information.

The first serving cell can be a primary serving cell, a licensedsecondary serving cell, an unlicensed secondary serving cell, and/or anyother cell. The second serving cell can be a licensed secondary servingcell, an unlicensed secondary serving cell, and/or any other cell. Thefirst and second serving cells can be the same serving cell or differentserving cells. Aperiodic subframes of cells can be aperiodic in thatthey do not follow a specific duty cycle.

At 230, the UE 110 can ascertain CSI-RS resources in a subframe of thesecond serving cell based on at least the DCI contents. CSI-RS resourcescan include at least a set of resource elements, antenna ports, ascrambling identifier (scrambling ID), and/or other resources for a UEto measure CSI. The subframe of an ascertained CSI-RS resource may ormay not be same subframe as the subframe in which the DCI is received.The ascertained CSI-RS resources in the subframe can also be based on ahigher layer signaled CSI-RS configuration for aperiodic CSI-RStransmission, where the higher layer can be a layer higher than aphysical layer. Higher layers can include a Radio Resource Control (RRC)layer, a Media Access Control (MAC) layer, and other layers higher thana physical layer.

At 250, the UE 110 can determine CSI based on the ascertained CSI-RSresources. At 260, the UE 110 can send the determined CSI to the basestation 120.

FIG. 3 is an example signal flow diagram 300 according to a possibleembodiment. The signal flow diagram 300 shows signals and operations ofthe first UE 110, the base station 120, and the second UE 112. Signalsfrom the signal flow diagram 300 can be performed in parallel with,sequential with, or in various orders with signals from the signal flowdiagram 200.

From the first UE 110 perspective, at 310 the first UE 110 can receiveZP-CSI-RS configuration information for an aperiodic ZP-CSI-RS of aserving cell. The aperiodic ZP-CSI-RS can be at least one aperiodicZP-CSI-RS of multiple aperiodic ZP-CSI-RS's. The ZP-CSI-RS's can beaperiodic in that they do not follow a specific duty cycle. TheZP-CSI-RS configuration information can include a bitmap, where each bitof the bitmap can correspond to a set of RE's. Each bit of the bitmapcan also indicate whether a given RE corresponds to a ZP-CSI-RS. Thisconfiguration can be signaled to the UE by the eNB via higher layersignaling, such as on a Radio Resource Control (RRC) layer. For example,higher layers can include a Radio Resource Control (RRC) layer, a MediaAccess Control (MAC) layer, and other layers higher than a physicallayer. The ZP-CSI-RS configuration information can be received in a DCI.

At 320, the first UE 110 can receive DCI on a physical control channelin a subframe of the serving cell. The DCI can indicate whether a PDSCHof the UE in the subframe of the serving cell is rate-matched aroundresource elements indicated by the ZP-CSI-RS configuration information.The DCI can include a field that indicates the ZP-CSI-RS configurationbased on which PDSCH is rate-matched in the subframe.

At 330, the first UE 110 can decode the PDSCH in the subframe of theserving cell based on rate-matching around the resource elementsindicated by the ZP-CSI-RS configuration when the DCI indicates thePDSCH of the first UE 110 is rate-matched around the resource elementsindicated by the ZP-CSI-RS configuration. The subframe of the PDSCH in330 can be the same subframe as the one in which the UE received the DCIin 320. Decoding can include receiving data on PDSCH after rate-matchingaround zero power RE's indicated by the ZP-CSI-RS configurationinformation. Rate-matching can include skipping resource elementsincluding a ZP-CSI-RS. For example, rate-matching can includedetermining whether PDSCH contents are not placed in or not mapped toRE's, i.e., determining which RE's do not include PDSCH contents.

At 340, the first UE 110 can receive a CSI-RS. At 350, the first UE 110can determine CSI based on a set of resource elements that is a subsetof resource elements indicated by the ZP-CSI-RS configurationinformation, such as based on the CSI-RS received in the subset ofresource elements. The subframe in 320 can be a first subframe and at360, the first UE 110 can send the determined CSI in a second subframe.The first subframe and the second subframe can be sequential or can beseparated by at least one intervening subframe or time period.Separating the first and second subframe can give a UE some processingtime to measure the RS and report it back to an eNB on the uplink. TheCSI can be computed using two components: a channel part which can bebased on a Non-Zero Power CSI-RS (NZP-CSI-RS) configuration, and aninterference part which can be based on a CSI-IM configuration, whichcan be similar to the NZP-CSI-RS configuration in structure, such as insignaling format.

From the base station 120 perspective, at 310, the base station 120 cansignal a ZP-CSI-RS configuration for an aperiodic ZP-CSI-RS for thefirst UE 110 via at least one higher layer, where the higher layer canbe higher than a physical layer. At 320, the base station 120 canindicate via a control channel to the first UE 110 in a subframe as towhether the first UE 110 rate-matches PDSCH around resource elementsindicated by a ZP-CSI-RS configuration for an aperiodic ZP-CSI-RS forthe first UE 110 via at least one higher layer. The base station 120 canindicate the rate-matching via a control channel of a first servingcell. The first serving cell can be a primary cell and the first UE 110can be connected to the primary cell. At 340, the base station 120 cantransmit a CSI-RS in resource elements that are subset of resourceelements indicated by the ZP-CSI-RS configuration.

At 370, the base station 120 can transmit an aperiodic CSI request to aUE. The UE 112 that the base station 120 transmits the aperiodic CSIrequest to can be the first UE 110 and/or the second UE 112. Theaperiodic CSI request can direct the first UE 110 and/or the second UE112 to measure CSI based on resource elements in the subframe that are asubset of the ZP-CSI-RS configuration. The aperiodic CSI request can bea request for CSI for resources elements that are aperiodic, such as foraperiodic CSI-RS's. The aperiodic CSI request can direct the first UE110 and/or the second UE 112 to measure CSI based on resource elementsin a subframe of a second serving cell where the resources elements area subset of the ZP-CSI-RS configuration. At 380, the base station 120can receive in another subframe, a message containing the requested CSIfrom the first UE 110 and/or the second UE 112.

Embodiments can provide for CSI enhancements for LTE operation inunlicensed spectrum, such as for Licensed Assisted Access for LTE(LAA-LTE) so that LAA-LTE can coexist of with other unlicensed spectrumdeployments and can provide physical layer options and enhancements toLTE to meet design targets and requirements.

Listen-Before-Talk (LBT) and discontinuous transmission requirements canbe used for operation in unlicensed spectrum, such as 5 GHz, (e.g. usedfor Wi-Fi), in some countries/regions. Modifications to physical layersignaling and assumptions from a base station to a user equipment (eNBto UE), as compared to the LTE Release 12 (Rel 12) standard, can beimplemented to operate LAA-LTE UEs in unlicensed spectrum with suchrequirements. The modifications can also help in improving LAA-LTE andWi-Fi coexistence on the same unlicensed carrier.

In LTE operation on a licensed carrier, signals, such as synchronizationsignals, Cell specific Reference Signals (CRS), CSI-RS, and CSI-IM, aretypically transmitted periodically, since the medium, i.e. frequencyspectrum, is always assumed to be available given the operator hasexclusive use of the spectrum. However, the medium on an unlicensedcarrier is not always available for an LTE operator. For example, thefrequency spectrum of an unlicensed carrier, such as the spectrum usedfor Wi-Fi, can be shared with other users. The physical layer design ofLTE can be adapted so that it can work on a medium that may be availablefor discontinuous time-periods and/or a medium that may not be with thesame periodicity as that for LTE operation on a licensed carrier.

For instance, for supplemental downlink using LTE in unlicensedspectrum, such as 5 GHz spectrum, where medium access is based on LBT,in some situations an eNB should perform a clear-channel assessment,such as energy detection, according to some requirements, such asregulatory, Clear Channel Assessment (CCA) per IEEE 802.11 standard,and/or other requirements, to detect if the medium is free. If the eNBdetects that medium is free, then the eNB can start transmitting signalsaccording to an LTE format, such as using an LTE subframe structure, forsome amount of time, such as a few milliseconds, before it has to giveup the medium and/or perform another CCA for accessing the medium.

Multiple techniques can be employed to use LTE in unlicensed spectrum.According to one technique, for LTE Rel10-12 Carrier Aggregation (CA) ordual connectivity, the eNB can configure a Secondary serving cell(Scell) to the UE to provide additional frequency resources, such as asecondary carrier or a secondary Component Carrier (CC), forcommunication in addition to a Primary serving cell (Pcell). For a UE,the unlicensed carrier can be utilized as a S cell in the carrieraggregation context, where the Pcell can be operating on a licensedcarrier, where both cross-carrier and same-carrier scheduling could besupported for the Scell. For convenience, a Scell operating inunlicensed carrier can be denoted as Scell-u. According to anothertechnique, the Scell-u can be aligned substantially in the time domainwith another cell, such as a Scell or a Pcell, at radio frame andsubframe level. According to another technique, the eNB can perform CCAto determine when the medium is free. If it determines the medium isfree, then it can transmit LTE signals on the Scell-u.

According to another technique, the UE may be using discovery signalsfor Radio Resource Management (RRM) measurements and reporting themeasurements on the unlicensed carrier, such as the corresponding toScell-u. Since discovery signals can occur with sparse periodicity, itmay be assumed that the discovery signals are always transmitted on anunlicensed carrier. For example, the discovery signals may not besubject to the LBT limitation. Alternatively, if the medium is notavailable at a particular discovery signal occasion, the correspondingdiscovery signals may be moved in time to a suitable time interval wherethe medium is available.

According to another technique, the eNB may need to create guardintervals, such as of <1 Orthogonal Frequency Division Multiplex (OFDM)symbol (which is typically around 70 microseconds), in its downlinktransmissions to the UEs. Since CCA duration can be ˜20 us, a guardperiod of 1 OFDM symbol of duration 70 us per current LTE framestructure may be useful to support CCA. This can be achieved by creatingshortened downlink subframes for UEs. For example, for Time DivisionDuplex (TDD) operation on a Scell-u, shortened uplink subframes may berequired, which can be achieved using a fake Sounding Reference Signal(SRS) symbol, such as by configuring the last symbol of the subframe asa SRS symbol instead of a CCA. Single symbol guard intervals occurringat the beginning of a subframe can be possible using cross-carrierscheduling, and using pdschStartSymbol=1 signaling for the unlicensedcarrier, assuming a subframe starts with symbol 0 numbering for thefirst symbol in the subframe. Single symbol guard intervals occurring atthe beginning of a subframe can be possible using self-carrierscheduling, Enhanced Physical Downlink Control Channel (EPDCCH), andusing epdcchStartSymbol>=1 signaling for the unlicensed carrier. Forsingle symbol guard intervals occurring at the end of the subframe, thedownlink subframe can be shortened and special subframe formats, such asdefined for TDD, can be used to create guard intervals in the downlinksubframes.

According to another technique, it may be useful to have the eNB maycreate guard intervals of length 1 ms or higher in its downlinktransmissions to the UEs. The guard interval can serve several purposes,such as to allow eNB to release the medium for a few subframes to meetthe channel occupancy requirements per the LBT specification, etc., andsuch as to allow eNB energy savings, interference reduction, etc. The UEcan be oblivious to the exact purpose of what the guard period is usedfor. This technique can use subframe-level ON/OFF for a UE that is inactivated state on the Scell.

According to another technique, for subframe-level ON/OFF, in theactivated state, the multiple aspects can be considered. According toone aspect, for Primary Synchronization Channel (PSS)/SecondarySynchronization Channel (SSS), given overhead is small, a UE may assumethat the REs corresponding to PSS/SSS are always occupied irrespectiveof whether the subframe is ON or OFF. Another option is to always assumethat PSS/SSS, except for those PSS/SSS that occur in Discovery signalsis not transmitted for Scells. Another option is for the UE in activatedstate to assume PSS/SSS is transmitted in predetermined synchronizationsubframes, such as subframe 0, 5 for Frequency Division Duplex (FDD),subframe 1, 6 for TDD, etc., only if a DCI format (PDCCH/EPDCCH) isdetected or PDSCH scheduled in that subframe. According to anotheraspect, for Cell-specific Reference Signal (CRS), if a UE detects andfinds a PDCCH/EPDCCH/PDSCH for the Scell in a subframe, the UE canassume the subframe is not OFF, such as assume a CRS is present in thesubframe. Otherwise, the UE can assume that CRS is not present in thesubframe. According to another aspect, a discovery signal may be alwaystransmitted irrespective of ON/OFF status of a subframe. Alternately, ifthe medium is busy, the discovery signal occasion can be moved to thenearest time duration when medium is available. Aperiodic discoverysignal scheduling can be possible. A discovery signal occasion caninclude a burst of PSS/SSS+CRS+CSI-RS every M milliseconds, where M canbe 40, 80 or 160. According to another aspect, for (E)PDCCH, a UE canblindly detect, or monitor a set of (E)PDCCH candidates, every subframeon the Scell to detect DCI. If the UE detects DCI in a subframe, the UEcan follow the DCI, and assume that the subframe is not OFF. Accordingto another aspect, for PDSCH, if the UE detects DCI scheduling PDSCH inthe Scell in a subframe, the UE can follow the DCI, and assume that thecorresponding Scell subframe is not OFF. The DCI may come fromself-scheduling or cross-carrier scheduling.

An issue can still remain on how to handle Channel State InformationReference Signal CSI-RS transmissions and CSI reporting based on CSI-RS.

One option to handle CSI-RS transmission for activated Scell ON/OFFoperation on a Scell-u can use a current periodic CSI-RS structure forCSI transmission and the eNB can occasionally drop CSI-RS in a subframeif the medium is not available. The UE can have multiple choices toreport CSI.

One way the UE can report CSI is to measure and report CSI assuming thatCSI-RS is always present periodically on the unlicensed carrier. In thiscase, the UE may be measuring and reporting just “noise” if the Scell isoff In this case, averaging measurements across multiple CSI-RSoccasions may not be used. Also, an ON/OFF Indicator or ON/OFF detectionmay not be required.

FIG. 4 is an example illustration of subframes 400 of another way a UEcan report CSI according to a possible embodiment. The subframes 400 caninclude subframes 410 transmitted in a downlink by an eNB Pcell,subframes 420 transmitted in a downlink by an eNB Scell, and subframes430 transmitted in an uplink by a UE. The subframes 420 can betransmitted in a downlink by an unlicensed eNB Scell. In thisembodiment, the UE can measure and report CSI assuming CSI-RS is presentonly in ON subframes, such as subframe 422, and use the CSI-RS of a mostrecent ON subframe to report CSI in a given uplink subframe 432. In thisembodiment, an ON/OFF Indicator or ON/OFF detection required may berequired. The UE can report CSI assuming CSI-RS is present only in ONsubframes. If the most recent subframe configured for CSI-RS is an OFFsubframe 424, the UE can report Out-Of-Range (OOR) in a given uplinksubframe 434. In this case, an ON/OFF Indicator or ON/OFF detection maybe required. This case may result in extra transmissions from the UE ona PUCCH from OOR transmissions. The UE can report out-of-range indicatorwith the smallest rank value to reduce uplink payload.

To improve the ‘ON/OFF indication’ approach, a maximum frame durationcan be configured and known to the UE. The maximum frame duration can bethe longest duration that the eNB can hold the medium. The eNB can sendan ‘ON’ indication via PCell when it acquires the channel UE can thenstart to measure and report CSI per configuration. After the maximumframe duration, the UE can stop measuring and reporting CSI. The UE canthen wait until it sees another ON indication. If another ON indicationis seen while the UE is measuring and reporting, a maximum frameduration timer can be reset, such as to the maximum frame duration. Ifthe eNB or Scell goes to OFF state early, the UE can continue measuringand reporting CSI, which would not pose a problem. This approach canmake it unnecessary to send ON/OFF indications every subframe. Only ONindications may be needed and only when the eNB acquires/reacquires themedium.

FIG. 5 is an example illustration of subframes 500 of another way a UEcan report CSI according to a possible embodiment. The subframes 500 caninclude subframes 510 transmitted in a downlink by an eNB Pcell,subframes 520 transmitted in a downlink by an eNB Scell, and subframes530 transmitted in an uplink by a UE. The subframes 520 can betransmitted in a downlink by an unlicensed eNB Scell.

This option for handling CSI-RS transmission for activated Scell ON/OFFoperation on a Scell-u can use an aperiodic CSI-RS structure for CSIwhere the CSI-RS can be dynamically scheduled, such as via a Pcell andusing cross-carrier scheduling. This option can relate to the signalflow diagram 200. A corresponding CSI reporting grant can be a broadcastgrant so that multiple UEs can measure CSI-RS and report the CSIaccording to their respective periodic/aperiodic CSI reporting schedule.The subframe 522 in which the CSI-RS is received can be considered to bethe “reference” subframe for CSI measurement, and the CSI can bereported in a subframe 532 on a PUCCH or a Physical Uplink SharedChannel (PUSCH). An aperiodic CSI request may also be sent by an eNB torequest the CSI aperiodically. According to a possible implementation,an aperiodic CSI request including a request of CSI for an Scell can bean indicator that CSI-RS is present on the SCell subframe including thecontrol channel in which the CSI request is sent.

FIG. 6 is an example illustration of subframes 600 of another way a UEcan report CSI according to a possible embodiment similar to theprevious embodiment. The subframes 600 can include subframes 610transmitted in a downlink by an eNB Pcell, subframes 620 transmitted ina downlink by an eNB Scell, and subframes 630 transmitted in an uplinkby a UE. The subframes 620 can be transmitted in a downlink by anunlicensed eNB Scell. This option for handling CSI-RS transmission foractivated Scell ON/OFF operation on a Scell-u can use aperiodic CSI-RSstructure for CSI, where the CSI-RS can be dynamically scheduled, suchas via a Pcell and using cross-carrier scheduling with somevalidity/expiry timer. The grant can be a broadcast grant so thatmultiple UEs can measure CSI-RS and report according to their respectiveperiodic CSI reporting schedule. This can allow an eNB to allow the CSIreports to be aligned with medium access boundaries. For instance, theeNB may request the UE to measure CSI in the last subframe of thecurrent medium access so that the eNB has some knowledge when it regainsmedium access in the next attempt. The reference subframes for CSImeasurements can be the subframes 622 and 624 in which the CSI-RS isreceived, and the CSI may be reported on the PUCCH or PUSCH 632. Anaperiodic CSI request may also be sent by the eNB to request the CSIaperiodically.

For unlicensed carriers, aperiodic CSI-RS can be scheduled for the UE inthe first subframe that begins after the medium is available. Severaloptions can be used to provide aperiodic CSI-RS transmission andreporting aperiodic CSI based on aperiodic CSI-RS transmission.According to a possible option, higher layers indicate number of CSI-RSantenna ports, resources (REs) and/or a power setting, such as theabsence of subframe-offset and periodicity, for one or more CSI-RSconfiguration, such as one or more CSI-RS resource configuration and oneor more CSI-IM resource configuration corresponding to one or more CSIprocesses and/or CSI subframe sets. This CSI-RS configuration can differfrom the Rel-11/12 CSI-RS configuration for CSI reporting in that thisCSI-RS configuration can indicate an aperiodic CSI-RS transmission, suchas due to absence of subframe-offset and/or periodicity. According toanother possible option, a separate aperiodic CSI reporting grant withits own Cyclic Redundancy Check (CRC), such as a CSI-Radio NetworkTemporary Identifier (CSI-RNTI), can be used for CSI-RS transmissions.The grant can explicitly indicate the CSI-RS resource and the uplinkresources, such as Resource Blocks (RBs), on which the CSI feedback istransmitted. The grant may be transmitted on the Pcell or Scell-u.According to another possible option, an aperiodic CSI-RS transmissionmessage, such as sent on physical control channel, can indicate whethera subframe contains the CSI-RS. According to another possible option, anaperiodic CSI-RS transmission message, such as sent on physical controlchannel, can indicate the subframes in which CSI-RS is transmitted. Themessage may be valid only for a certain number of subframes, such as 10subframes, and may indicate a subframe subset, such as subframe 0, 4, 8,that can have CSI-RS within a limited time period. This message canrefer to CSI-RS in multiple subframes. According to another possibleoption, the CSI-RS configuration can also include separate channelmeasurement RS and interference measurement resources. According toanother possible option, when sending a CQI based on measuring a desiredsignal and interfering signal, the RE's on which the desired signal isretrieved can be different than the RE's on which the interference ismeasured.

For the timing between the transmission of aperiodic CSI request andcorresponding CSI-RS transmission/measurement subframe, an aperiodic CSIrequest DCI for an Scell-u received in subframe n can imply varioustypes of information to a UE. For example, it can imply that subframe ncontains CSI-RS for Scell-u, where the CSI-RS configuration can be a newRel-13 CSI-RS configuration indicated by higher layers that includesRE's, antenna ports, and/or a power setting, such as an absence ofsubframe-offset and periodicity.

An aperiodic CSI request DCI for an Scell-u received in subframe n canalso imply that subframe n contains CSI-RS according to a CSI-RSconfiguration X, where the CSI-RS configuration X can be selected from aset of new Rel-13 CSI-RS configurations configured by higher layers thatinclude includes RE's, antenna ports, and/or a power setting, such asthe absence of subframe-offset and periodicity. The configuration X canbe indicated in the DCI requesting the aperiodic CSI-RS request. Forexample, two bits in DCI can be used to signal one of four CSI-RSconfigurations including no aperiodic CSI trigger, such as shown inTable 1.

TABLE 1 CSI-RS Indicator field for aperiodic CSI-RS configuration Valueof CSI-RS Indicator field Description ‘00’ No aperiodic CSI report istriggered ‘01’ Aperiodic CSI report is triggered for a 1st CSI-RSconfiguration for serving cell u ‘10’ Aperiodic CSI report is triggeredfor a 2nd set of CSI- RS configuration for serving cell u ‘11’ AperiodicCSI report is triggered for a 3rd set of CSI- RS configuration forserving cell u

The CSI-RS configuration can also include separate channel measurementCSI-RS and interference measurement resources.

Besides aperiodic CSI request in uplink DCI format and Random AccessResponse (RAR) grants that are supported in LTE, the aperiodic CSIrequest can be triggered from DCI formats used for Downlink (DL) datascheduling on Scell-u in a subframe. The aperiodic CSI report can betriggered for a set of CSI process(es) and/or {CSI process, CSI subframeset}-pair(s) configured by higher layers for serving cell u and can bereported on a higher-layer configured uplink resource according to ahigher-layer configured CSI-RS configuration in the subframe. Two bitsin DCI may be used to signal whether aperiodic CSI is triggered andselecting one of three uplink resources configured by higher layers,such as according to the mapping in Table 2.

TABLE 2 CSI request field and Physical Uplink Shared Channel (PUSCH)resource for Aperiodic CSI (can be extra with Table 1). Value of CSIrequest field Description ‘00’ No aperiodic CSI report is triggered ‘01’Aperiodic CSI report is triggered for a set of CSI process(es) and/or{CSI process, CSI subframe set}-pair(s) configured by higher layers forserving cell c and on a first PUSCH resource configured by the higherlayers ‘10’ Aperiodic CSI report is triggered for a set of CSIprocess(es) and/or {CSI process, CSI subframe set}-pair(s) configured byhigher layers for serving cell c and on a second PUSCH resourceconfigured by the higher layers ‘11’ Aperiodic CSI report is triggeredfor a set of CSI process(es) and/or {CSI process, CSI subframeset}-pair(s) configured by higher layers for serving cell c and on athird PUSCH resource configured by the higher layers

The dynamic resource configuration of CSI-RS described in Table 1 can becombined with the dynamic uplink resource configuration in Table 2, forexample, as a separate bit-field or a jointly-encoded bit-field.

A possible embodiment can provide a Zero Power-CSI-RS (ZP-CSI-RS)indicator in DCI formats for downlink transmission modes 1 to 10,TM1-10. A UE may be configured by higher layers in one out of thevarious transmission modes. Each transmission mode has associated set ofDCI formats and PDSCH transmission scheme/schemes, such as singleantenna port transmission based on CRS, transmit diversity based on CRS,open loop MIMO based on CRS, closed loop MIMO based on CRS, closed loopMIMO based on UE-specific demodulation reference signals, etc. Thisembodiment can relate to the signal flow diagram 200. For example,whenever CSI-RS is scheduled aperiodically in a subframe, it can also beuseful to ensure that UEs can receive data in that subframe irrespectiveof whether an aperiodic CSI request is triggered for a given UE. Thiscan imply that the Physical Downlink Shared Channel (PDSCH) should berate-matched around the aperiodic CSI-RS. This can be done by creating anew dynamic ZP-CSI-RS indicator field that is sent via DCI formats usedfor DL data scheduling in all transmission modes. For TM10, whichcorresponds to PDSCH based on UE-specific DMRS, this can be achieved byadding another ZP-CSI-RS indicator field in the DCI formats used for DLdata scheduling or by adding a Rel-13 ZP-CSI-RS indicator to the PDSCHRate Matching and QuasiCoLocation Indicator (PQI) fields in DCI format2D. Example values of the indicator field and corresponding descriptionsare shown in Table 3. TM10 is defined typically for supportingcoordinated multipoint transmission, using PDSCH transmission schemesbased on UE-specific DMRS.

TABLE 3 Dynamic ZP-CSI-RS Rate-matching parameter. Value of ZP-CSI- RSindicator field Description ‘00’ No additional ZP-CSI-RS REs indicatedby the DCI ‘01’ PDSCH is rate-matched around first set of dynamic ZP-CSI-RS REs in the subframe ‘10’ PDSCH is rate-matched around second setof dynamic ZP-CSI-RS REs in the subframe ‘11’ PDSCH is rate-matchedaround third set of dynamic ZP- CSI-RS REs in the subframe

Rate matching can mean skipping the ZP-CSI-RS RE's for data, butmeasuring the CSI-RS if instructed to.

For PDSCH demodulation in TM10, the antenna port(s) on which aDemodulation Reference Signal (DMRS) are transmitted is assumed to bequasi co-located with CSI-RS antenna ports, such as the antenna port onwhich CSI-RS is transmitted, corresponding to an indicated CSI-RSresource configuration. An antenna port can be defined such that thechannel over which a symbol on the antenna port is conveyed can beinferred from the channel over which another symbol on the same antennaport is conveyed. Two antenna ports can be said to be quasi co-locatedif the large-scale properties of the channel over which a symbol on oneantenna port is conveyed can be inferred from the channel over which asymbol on the other antenna port is conveyed. The large-scale propertiescan include one or more of delay spread, Doppler spread, Doppler shift,average gain, and average delay.

If CSI-RS is transmitted aperiodically, then other than CSI feedback,CSI-RS signals can also be used for quasi-colocation purposes, such asfor determining the large scale properties of the channel In this case,there it can be useful to use an explicit indication of CSI-RStransmissions. The CSI-RS resource configuration can be indicated forquasi-colocation with Demodulation Reference Signal (DM-RS). The UE canuse measurements on one or more CSI-RS corresponding to previousaperiodic CSI request triggers associated with the indicated CSI-RSconfiguration for quasi co-location purposes. The UE can be configuredto assume that one or more of the antenna port(s) corresponding to theCSI-RS resource configuration(s) as part of the discovery signals, suchas within the discovery signal occasion for the cell, for which the UEcan assume non-zero transmission power for the CSI-RS and the DM-RSantenna ports associated with the PDSCH are quasi co-located.Alternatively, or in addition, the UE can be configured to assume thatthe CRS antenna port transmission as part of the discovery signalswithin the discovery signal occasion for the cell and the DM-RS antennaports associated with the PDSCH are quasi co-located.

The following Quasi-Co-Location (QCL) indicator relationship can be usedfor PDSCH based on TM10 in Rel-11 where

can indicate that the corresponding antenna ports are quasi co-located:

-   -   DMRS        periodic CSI-RS resource        periodic CRS (cell-ID, Number of antenna ports, MBSFN pattern,        etc).

If both CSI-RS and CRS are sparse, such as transmitted aperiodically,then the QCL relationship can be:

-   -   DMRS        aperiodic CSI-RS resource        Discovery signal (or a subset CRS/CSI-RS of the discovery        signal).

FIG. 7 is an example block diagram of an apparatus 700, such as the UE110 or the UE 112, according to a possible embodiment. The apparatus 700can include a housing 710, a controller 720 within the housing 710,audio input and output circuitry 730 coupled to the controller 720, adisplay 740 coupled to the controller 720, a transceiver 750 coupled tothe controller 720, an antenna 755 coupled to the transceiver 750, auser interface 760 coupled to the controller 720, a memory 770 coupledto the controller 720, and a network interface 780 coupled to thecontroller 720. The apparatus 700 can perform the methods described inall the embodiments.

The display 740 can be a viewfinder, a liquid crystal display (LCD), alight emitting diode (LED) display, a plasma display, a projectiondisplay, a touch screen, or any other device that displays information.The transceiver 750 can include a transmitter and/or a receiver. Theaudio input and output circuitry 730 can include a microphone, aspeaker, a transducer, or any other audio input and output circuitry.The user interface 760 can include a keypad, a keyboard, buttons, atouch pad, a joystick, a touch screen display, another additionaldisplay, or any other device useful for providing an interface between auser and an electronic device. The network interface 780 can be auniversal serial bus port, an Ethernet port, an infraredtransmitter/receiver, a USB port, an IEEE 1397 port, a WLAN transceiver,or any other interface that can connect an apparatus to a network orcomputer and that can transmit and receive data communication signals.The memory 770 can include a random access memory, a read only memory,an optical memory, a flash memory, a removable memory, a hard drive, acache, or any other memory that can be coupled to a wirelesscommunication device.

The apparatus 700 or the controller 720 may implement any operatingsystem, such as Microsoft Windows®, UNIX®, or LINUX®, Android™, or anyother operating system. Apparatus operation software may be written inany programming language, such as C, C++, Java or Visual Basic, forexample. Apparatus software may also run on an application framework,such as, for example, a Java® framework, a .NET® framework, or any otherapplication framework. The software and/or the operating system may bestored in the memory 770 or elsewhere on the apparatus 700. Theapparatus 700 or the controller 720 may also use hardware to implementdisclosed operations. For example, the controller 720 may be anyprogrammable processor. Disclosed embodiments may also be implemented ona general-purpose or a special purpose computer, a programmedmicroprocessor or microprocessor, peripheral integrated circuitelements, an application-specific integrated circuit or other integratedcircuits, hardware/electronic logic circuits, such as a discrete elementcircuit, a programmable logic device, such as a programmable logicarray, field programmable gate-array, or the like. In general, thecontroller 720 may be any controller or processor device or devicescapable of operating an electronic device and implementing the disclosedembodiments.

In operation, the transceiver 750 can receive DCI containing a CSIrequest on a physical control channel in a subframe of a first servingcell. The CSI request can direct the apparatus 700 to perform CSImeasurements for at least one aperiodic CSI-RS of a second serving cell.The DCI can also indicate granted resources on which the CSI is sent bythe apparatus 700 to the base station. The controller 720 can ascertainCSI-RS resources in a subframe of the second serving cell based on atleast the DCI contents and configured to determine CSI based on theascertained CSI-RS resources. The transceiver 750 can send thedetermined CSI to a base station.

According to another possible embodiment, the transceiver 750 canreceive ZP-CSI-RS configuration information for an aperiodic ZP-CSI-RSof a serving cell. The transceiver 750 can also receive DCI on aphysical control channel in a subframe of the serving cell. The DCI canindicate whether a PDSCH of the UE in the subframe of the serving cellis rate-matched around resource elements indicated by the ZP-CSI-RSconfiguration information. The controller 720 can decode the PDSCH inthe subframe of the serving cell based on rate-matching around theresource elements indicated by the ZP-CSI-RS configuration when the DCIindicates the PDSCH of the UE is rate-matched around the resourceelements indicated by the ZP-CSI-RS configuration.

FIG. 8 is an example block diagram of a base station 800, such as theeNB 120, according to a possible embodiment. The base station 800 mayinclude a controller 810, a memory 820, a database interface 830, atransceiver 840, Input/Output (I/O) device interface 850, a networkinterface 860, and a bus 870. The base station 800 can implement anyoperating system, such as Microsoft Windows®, UNIX, or LINUX, forexample. Base station operation software may be written in anyprogramming language, such as C, C++, Java or Visual Basic, for example.The base station software can run on an application framework, such as,for example, a Java® server, a .NET® framework, or any other applicationframework.

The transceiver 840 can create a data connection with the UE 110. Thecontroller 810 can be any programmable processor. Disclosed embodimentscan also be implemented on a general-purpose or a special purposecomputer, a programmed microprocessor or microprocessor, peripheralintegrated circuit elements, an application-specific integrated circuitor other integrated circuits, hardware/electronic logic circuits, suchas a discrete element circuit, a programmable logic device, such as aprogrammable logic array, field programmable gate-array, or the like. Ingeneral, the controller 810 can be any controller or processor device ordevices capable of operating a base station and implementing thedisclosed embodiments.

The memory 820 can include volatile and nonvolatile data storage,including one or more electrical, magnetic, or optical memories, such asa Random Access Memory (RAM), cache, hard drive, or other memory device.The memory 820 can have a cache to speed access to specific data. Thememory 820 can also be connected to a Compact Disc-Read Only Memory(CD-ROM), Digital Video Disc-Read Only memory (DVD-ROM), DVD read writeinput, tape drive, thumb drive, or other removable memory device thatallows media content to be directly uploaded into a system. Data can bestored in the memory 820 or in a separate database. For example, thedatabase interface 830 can be used by the controller 810 to access thedatabase. The database can contain any formatting data to connect theterminal 110 to the network 130.

The I/O device interface 850 can be connected to one or more input andoutput devices that may include a keyboard, a mouse, a touch screen, amonitor, a microphone, a voice-recognition device, a speaker, a printer,a disk drive, or any other device or combination of devices that acceptinput and/or provide output. The I/O device interface 850 can receive adata task or connection criteria from a network administrator. Thenetwork connection interface 860 can be connected to a communicationdevice, modem, network interface card, a transceiver, or any otherdevice capable of transmitting and receiving signals to and from thenetwork 130. The components of the base station 800 can be connected viathe bus 870, may be linked wirelessly, or may be otherwise connected.

Although not required, embodiments can be implemented usingcomputer-executable instructions, such as program modules, beingexecuted by an electronic device, such as a general purpose computer.Generally, program modules can include routine programs, objects,components, data structures, and other program modules that performparticular tasks or implement particular abstract data types. Theprogram modules may be software-based and/or may be hardware-based. Forexample, the program modules may be stored on computer readable storagemedia, such as hardware discs, flash drives, optical drives, solid statedrives, CD-ROM media, thumb drives, and other computer readable storagemedia that provide non-transitory storage aside from a transitorypropagating signal. Moreover, embodiments may be practiced in networkcomputing environments with many types of computer systemconfigurations, including personal computers, hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network personal computers, minicomputers, mainframecomputers, and other computing environments.

In operation, the controller 810 can control operations of the apparatus800. The transceiver 840 can transmit, to a UE, DCI containing a CSIrequest on a physical control channel in a subframe of a first servingcell. The CSI request can direct the UE to perform CSI measurements forat least one aperiodic CSI-RS of a second serving cell. The DCI caninclude an indication of resources for the aperiodic CSI-RS in asubframe of the second serving cell. The transceiver 840 can receive,from the UE, in another subframe, a message containing the requestedCSI. The controller 810 can also perform a LBT procedure to determine ifa carrier is clear for a carrier frequency corresponding to the secondserving cell prior to sending the aperiodic CSI-RS on the second servingcell.

In operation according to another possible embodiment, the transceiver840 can signal a ZP-CSI-RS configuration for an aperiodic ZP-CSI-RS fora first UE via at least one higher layer, where the higher layer can behigher than a physical layer. The transceiver 840 can indicate via acontrol channel to the first UE in a subframe as to whether the first UErate-matches PDSCH around resource elements indicated by a ZP-CSI-RSconfiguration for an aperiodic ZP-CSI-RS for the first UE via at leastone higher layer. The transceiver 840 can transmit a CSI-RS in resourceelements that are subset of resource elements indicated by the ZP-CSI-RSconfiguration. The transceiver 840 can transmit an aperiodic CSI requestto a UE, the aperiodic CSI request directing the UE to measure CSI basedon resource elements in the subframe that are a subset of the ZP-CSI-RSconfiguration, where the UE in this step can be the original UE or adifferent UE in earlier steps.

FIG. 9 is an example illustration of a subframe 900 according to apossible embodiment. The subframe 900 can include at least one resourceblock 910 including a plurality of resource elements 920. The subframe900 can include resource elements 930 of a first CSI-RS configuration.The subframe 900 can include resource elements 940 of a first CSI-RSconfiguration. The subframe 900 can also include resource elements 950indicated by a ZP-CSI-RS configuration. It should be noted that thesubframe 900 only shows resource elements for CSI-RS configurations andZP-CSI-RS configurations for conceptual purposes and understanding ofconcepts of the disclosed embodiments and does not necessarily representan actual subframe, resource elements, CSI-RS configurations, andZP-CSI-RS configurations.

Embodiments can provide for a base station that dynamically schedulesCSI-RS in a subframe for a UE. According to some embodiments a UE canreceive, from a base station, an aperiodic CSI request on a controlchannel in a subframe requesting CSI feedback for a serving cell. The UEcan determine the CSI-RS resources in the subframe based on the controlchannel contents. The UE can determine CSI information based on thedetermined CSI-RS resources. The UE can then send the CSI information tothe base station.

According to some embodiments, a base station can configure an aperiodicZP-CSI-RS configuration and subframe offset for a UE via higher layersthan a physical layer. The base station can indicate to the UE in asubframe via a control channel whether the UE rate-matches PDSCH aroundthe resource elements indicated by the ZP-CSI-RS configuration in thesubframe. The base station can transmit a CSI-RS in the resourceelements that are subset of REs indicated by the ZP-CSI-RS configurationin the subframe. The base station can transmit an aperiodic CSI requestto a second UE. The aperiodic CSI request can indicate, such as director request, the second UE to measure CSI based on resource elements inthe subframe that are a subset of the ZP-CSI-RS configuration.

According to some embodiments, a UE can receive an aperiodic CSI requeston a control channel in a subframe, where the CSI request requests CSIfeedback for a serving cell. The UE can determine the CSI-RS resourcesfor the serving cell are present in the subframe based on receivedaperiodic CSI request. The UE can determine CSI information based onCSI-RS resources for the serving cell in the subframe. The UE can thensend the CSI information to the base station in a second subframe.

According to some embodiments, a UE can be configured with an aperiodicZP-CSI-RS configuration and subframe offset via higher layers. The UEcan also be configured with an aperiodic CSI-RS configuration andsubframe offset via higher layers, where the RE's of CSI-RS can be asubset of RE's of ZP-CSI-RS. In a subframe a control channel a basestation can indicate to the UE whether its PDSCH is rate-matched aroundthe resource elements indicated by the ZP-CSI-RS configuration. In thesame subframe, the UE can receive a CSI-RS in RE's that are subset ofRE's indicated by the ZP-CSI-RS configuration. The UE can receive anaperiodic CSI request. The aperiodic CSI request can indicate, such asdirect or request, the UE to measure CSI based on RE's indicated by theCSI-RS configuration in the subframe in which the CSI request wasreceived. The UE can determine CSI information based on CSI-RS resourcesfor the serving cell in the subframe, and send the CSI information tothe base station in a second subframe.

The method of this disclosure can be implemented on a programmedprocessor. However, the controllers, flowcharts, and modules may also beimplemented on a general purpose or special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit elements, an integrated circuit, a hardware electronic or logiccircuit such as a discrete element circuit, a programmable logic device,or the like. In general, any device on which resides a finite statemachine capable of implementing the flowcharts shown in the figures maybe used to implement the processor functions of this disclosure.

While this disclosure has been described with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art. For example,various components of the embodiments may be interchanged, added, orsubstituted in the other embodiments. Also, all of the elements of eachfigure are not necessary for operation of the disclosed embodiments. Forexample, one of ordinary skill in the art of the disclosed embodimentswould be enabled to make and use the teachings of the disclosure bysimply employing the elements of the independent claims. Accordingly,embodiments of the disclosure as set forth herein are intended to beillustrative, not limiting. Various changes may be made withoutdeparting from the spirit and scope of the disclosure.

In this document, relational terms such as “first,” “second,” and thelike may be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The phrase“at least one of” followed by a list is defined to mean one, some, orall, but not necessarily all of, the elements in the list. The terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “a,” “an,” or the like does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that comprises the element. Also, the term“another” is defined as at least a second or more. The terms“including,” “having,” and the like, as used herein, are defined as“comprising.” Furthermore, the background section is written as theinventor's own understanding of the context of some embodiments at thetime of filing and includes the inventor's own recognition of anyproblems with existing technologies and/or problems experienced in theinventor's own work.

1. A method in a base station comprising: signaling a zero power channelstate information reference signal configuration for an aperiodic zeropower channel state information reference signal for a first userequipment via at least one higher layer, where the higher layer ishigher than a physical layer; indicating via a control channel to thefirst user equipment in a subframe as to whether the first userequipment rate-matches physical downlink shared channel around resourceelements indicated by a zero power channel state information referencesignal configuration for an aperiodic zero power channel stateinformation reference signal for the first user equipment via at leastone higher layer; transmitting a channel state information referencesignal in resource elements that are subset of resource elementsindicated by the zero power channel state information reference signalconfiguration; and transmitting an aperiodic channel state informationrequest to a user equipment, the aperiodic channel state informationrequest directing the second user equipment to measure channel stateinformation based on resource elements in the subframe that are a subsetof the zero power channel state information reference signalconfiguration, where the user equipment is one of the first userequipment and a second user equipment.
 2. The method according to claim1, further comprising: receiving, from the one of the first userequipment and the second user equipment, in another subframe, a messagecontaining the requested channel state information.
 3. The methodaccording to claim 1, further comprising sending channel stateinformation reference signal configuration information for an aperiodicchannel state information reference signal corresponding to theaperiodic channel state information request.
 4. The method according toclaim 1, wherein the subframe comprises a first subframe, and whereinthe method further comprises receiving channel state information in asecond subframe in response to transmitting the aperiodic channel stateinformation request.
 5. The method according to claim 1, whereinindicating comprises indicating via a control channel of a first servingcell, and wherein transmitting the aperiodic channel state informationrequest comprises transmitting an aperiodic channel state informationrequest to a second user equipment, the aperiodic channel stateinformation request directing the second user equipment to measurechannel state information based on resource elements in a subframe of asecond serving cell where the resources elements are a subset of thezero power channel state information reference signal configuration. 6.The method according to claim 5, wherein the first serving cell is aprimary cell and the user equipment is connected to the primary cell. 7.The method according to claim 1, further comprising: transmittingchannel state information reference signal configuration information fora channel state information reference signal of the serving cell,wherein a set of resource elements used for determining channel stateinformation is indicated by the channel state information referencesignal configuration information.
 8. The method according to claim 1,further comprising: transmitting channel state information interferencemeasurement configuration information for a channel state informationinterference measurement of the serving cell, wherein a set of resourceelements used for determining channel state information is indicated bythe channel state information interference measurement configurationinformation.
 9. The method according to claim 1, wherein the downlinkcontrol information includes a field that indicates the zero powerchannel state information reference signal configuration based on whichphysical downlink shared channel is rate-matched in the subframe. 10.The method according to claim 1, wherein rate-matching comprisesskipping resource elements including a Zero Power Channel StateInformation Reference Signal.
 11. An apparatus comprising: a controllerconfigured to control operations of the apparatus; and a transceivercoupled to the controller, the transceiver configured to signal a zeropower channel state information reference signal configuration for anaperiodic zero power channel state information reference signal for auser equipment via at least one higher layer, where the higher layer ishigher than a physical layer; the transceiver configured to indicate viaa control channel to the user equipment in a subframe as to whether theuser equipment rate-matches physical downlink shared channel aroundresource elements indicated by a zero power channel state informationreference signal configuration for an aperiodic zero power channel stateinformation reference signal for the user equipment via at least onehigher layer; the transceiver configured to transmit a channel stateinformation reference signal in resource elements that are subset ofresource elements indicated by the zero power channel state informationreference signal configuration; and the transceiver configured totransmit an aperiodic channel state information request to the userequipment, the aperiodic channel state information request directing theuser equipment to measure channel state information based on resourceelements in the subframe that are a subset of the zero power channelstate information reference signal configuration.